Urban Australian cities under termite attack

Urban Australian cities under termite attack
Barry Noller
National Research Centre for Environmental Toxicology, University of Queensland
Email: b.noller@uq.edu.au
Dale Gilbert
Department of Public Works
Email: dale.gilbert@publicworks.qld.gov.au
Ross Sadler
Qld Health Scientific Services
Email: Ross_Sadler@health.qld.gov.au
Rowan Truss
School of Engineering, University of Queensland
Email: r.truss@uq.edu.au
Myron Zalucki
School of Integrative Biology, University of Queensland
Email: m.zalucki@uq.edu.au
Des Connell
Griffith University
Email: d.connell@griffith.edu.au
Barry Chiswell
National Research Centre for Environmental Toxicology – The University of Queensland
39 Kessels Road Coopers Plains Qld 4108
Email : chiswell@uq.edu.au
Aaron Stewart
National Research Centre for Environmental Toxicology, University of Queensland
Email: a.d.stewart@uq.edu.au
Sharad Rajendran
School of Engineering – The University of Queensland St Lucia Qld 4072
Email : s.rajendran@minmet.uq.edu.au
Amanda Hasthorpe
National Research Centre for Environmental Toxicology, University of Queensland
Email: a.hasthorpe@uq.edu.au
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Urban Australian cities under termite attack
ABSTRACT
There is an emerging huge cost to buildings and other wooden structures from termite damage in
urban Australia. Concerns about the environmental and public health consequences of the large
quantity and frequent reapplication of termiticides (chemicals for the treatment of termites) in urban
Australia has led stakeholders to identify a need to have appropriate information that reflects local
conditions about their environmental and health effects. There are costs associated with the
prevention and treatment of termite infestation in wooden structures. Reapplication of chemical
barriers is required every 2 to 5 years depending on the products used and local conditions.
Currently in urban Australia, we have been enjoying a period of overlap where older buildings are
still being protected by the organochlorines while new structures are treated with organophosphates
or pyrethroids. However, the effectiveness of the residual organochlorines is now reducing, and
older houses may be at risk of termite infestation. The potential costs of re-treatment and repairs are
likely to increase dramatically in the future as older slab-on-ground dwellings become susceptible
due to the eventual breakdown of the organochlorine termiticides.
It is critical to identify information gaps between current acceptable industry practice for termite
management in urban locations and public concerns. This may be achieved by recognising gaps in
knowledge of each component of termite management, from termite ecology through to the present
and future use of termiticides, and identifying these in terms of industry, public and client priorities.
A review on aspects of environmental effects of currently used termiticides, along with a review of
previous, current and future termiticides in the context of appropriate techniques for termite
management and client priorities has identified several requirements including the following: (i)
Further information on Australian termite biology, taxonomy, ecology and behaviour; (ii) Improved
definition of the problem of termite infestation needs to be defined, locally and nationally; (iii)
Identification of high-risk structures and building types, so that preventive measures can be taken in
terms of design and construction; and (iv) Further education for homeowners, builders, designers,
legislators and landscape designers in terms of practices in landscaping and design that
inadvertently favour termites. Such approaches provide a pathway to deal with the “attack” by
termites on buildings in urban Australia.
INTRODUCTION
Termites consume wood and cellulose in natural bush land and serve an important ecological
function by converting dead trees into organic matter. Unfortunately in the urban environment, the
wood in buildings and other structures such as wooden power poles and bridges is equally
appealing to termites and infestation can cause considerable damage. During the 1999–2000
financial year, the Queensland Department of Housing spent $410,000 managing termite
infestations in public housing. In the Ipswich, Woodridge and Capalaba areas in southeast
Queensland, the estimated cost of repairs for termite damage ranged from $18,000 to $60,000 per
property (Department of Public Works’ Built Environment Research Unit figures, September 2005).
On average, termite infestations cost approximately $1500 in treatment, and repairs of $5000 for
each building affected (Caulfield, 2002). It is estimated that 10% of Australian houses have had or
will have termite infestations, with that figure rising to 65% in some areas – a resulting per annum
cost of $4 billion (Caulfield, 2002). Management of termites, and eradication of exotic species is
also costly – a campaign to eradicate West Indian dry wood termite Cryptotermes brevis (Walker)
in Queensland is estimated to have cost $4.2 million by 1998 (Peters and Fitzgerald, 1998).
Worldwide, damage caused by termites is estimated at U.S $22 billion per annum in terms of
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damage to wooden structures (Fage et al., 1988). Treatment and prevention of termite damage in
Australian cities is therefore needed, and may give rise to unwanted side effects (Figure 1).
Until 1995, organochlorine termiticide treatments were used to create barriers to termites in
Australia. These have since been replaced with other, less persistent, chemicals and physical
barriers. As a consequence, chemical termiticides need to be reapplied on a regular basis, averaging
every 3 to 5 years depending on local conditions. There is a relative lack of knowledge of the
consequences of repeatedly using these replacement chemicals under Australian conditions (Boyd
et al., 2003). In 2005, bifenthrin (FMC Australasia Pty Ltd) is the most commonly used termiticide
in Australia followed by imidacloprid and fipronil. Chlorpyrifos (Dow Agricultural Products) has
decreased in use because of concerns over toxicity and efficacy in alkaline soils (Boyd et al., 2003).
Permethrin, alpha-cypermethrin are not currently used even though they remain registered for use in
Australia by the National Registration Authority (NRA).
Thus a key problem is identified with respect to building and housing protection in Australian cities
from termite attack. This attack is expected to increase due to the apparent decline in effectiveness
of the organochlorines that were applied prior their use being banned.
Termite Ecology
Australia’s termite fauna is diverse, represented by five families (Mastotermitidae, Termopsidae,
Kalotermitidae, Rhinotermitidae and Termitidae) comprising 40 known genera and more than 266
described species. Termites play a key role in the nutrient cycles of tropical ecosystems (Whitford,
1991). Termites may be grouped as damp wood, dry wood or subterranean, depending on their
habits. Damp wood termites live in rotten wood, particularly in logs or in damp sections of trees and
are rarely considered to be of economic concern. Certain dry wood termites are of economic
importance, with the exotic West Indian dry wood termite C. brevis identified as the most
destructive species (Peters and Fitzgerald, 1998). Subterranean termites are those that require
contact with the ground or moisture and they are responsible for damage to timber structures in
buildings and in trees.
In Australia, the majority of pest termites are native (the exception is C. brevis) (Boyd et al., 2003).
They are well adapted to local conditions and may be quite resistant to treatments. Relatively few
Australian termites are considered to be pests of sound timber, with the most economically
important being Mastotermes darwiniensis (Froggatt), Coptotermes acinaciformis (Froggatt),
Coptotermes frenchi Hill, Coptotermes raffrayi Wasmann, Coptotermes michaelseni Silvestri,
Schedorhinotermes reticulatus (Froggatt), Schedorhinotermes seclusus (Hill), Schedorhinotermes
intermedius (Brauer), Schedorhinotermes actuosus Hill, Heterotermes platycephalus Froggatt,
Heterotermes paradoxus (Froggatt), and Nasutitermes exitiosus (Hill) (Hill, 1942, Peters et al.,
1996, Postle & Abbott, 1991).
Subterranean termites forage for food by means of covered runways (or galleries), which extend
from the central nest to food sources above or below ground (up to 95m away) (Miller, 1993).
Colonies consist of distinct castes, each performing a specialised task within the colony. Workers
provide food for the colony, feed the other caste members and excavate galleries, while soldier
termites defend the colony and tend to be equipped with mandibles or a proboscis (depending on the
species) for defence. Reproductives are winged, and tend to swarm after summer rains to establish
new colonies. On returning to the ground the reproductives shed their wings and search for food and
moisture in the soil. After digging a chamber near a food source, the pair mate and a colony is
begun. Supplemental reproductives can be formed in some species within 3 to 4 months after
separation from the founding colony (Pawson & Gold, 1996), making it important not to fractionate
the colony during management procedures.
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Figure 1 Examples of termite damage. Photos courtesy of Amalgamated Pest Control.
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HISTORICAL TERMITE MANAGEMENT IN AUSTRALIA
In Australia prior to 1962, arsenic dusting was the most common means of small-scale termite
management. Nests were located and dusted directly with arsenic trioxide powder. Before 1995,
subterranean termite management in Australia was based on the use of the highly persistent
organochlorine insecticides ( Peters & Fitzgerald, 1988), such as aldrin, dieldrin, chlordane and
heptachlor (known collectively as cyclodienes, because of their particular chemical structure),
which were well suited to slab-on-ground housing construction. Because of their chemical stability,
they were extremely effective Australia-wide, and had no immediate adverse health effects at the
levels of exposure arising from the approved use. Owing to environmental and public health
concerns associated with their persistence in the environment and their tendency to accumulate in
the fat of animals and humans, these chemicals were withdrawn from the market in 1995 and
alternative strategies for termite management have been developed (Boyd et al., 2003).
Organochlorines used under slabs offered protection from termites for up to 30 years, and pretreated wood for up to 10 years (Boyd et al., 2003). For some species organochlorine baits (Mirex)
were used with success. The Northern Territory and Western Australia received an extension to use
of organochlorines in the form of Mirex and Mirant baits for M. darwiniensis management only,
until June 2003. These products were largely used for prevention of termite infestation of fruit trees
in orchards.
Currently in Australia, we may be enjoying a period of overlap where older buildings are still being
protected by the organochlorines while new structures have been treated variously with
organophosphates (chlorpyrifos), pyrethroids (bifenthrin) and imidocloprid. Houses built before
1985 may still be protected to some extent by the organochlorine termiticides applied to the soil
during construction. However, the effectiveness of the residual organochlorines will have been
reducing over time (possibly up to 20 years although there is no reliable Australian data), and older
houses may be at risk of termite infestation. The potential costs of re-treatment and repairs are
likely to increase dramatically in the future as older slab-on-ground dwellings become susceptible
due to the eventual failure of the organochlorine termiticides.
The success of the organochlorines over long periods of time has added to the popularity of slab-onground housing in Australia, buildings which are much more susceptible to infestation by termites
than older style above-ground housing (Boyd et al., 2003). This means that the potential for termite
damage is increased. The result of Australia’s previous reliance on the highly persistent
organochlorines is that modern housing is quite susceptible to attack by termites, with termites
entering buildings through weepholes, expansion joints, service ducts and cracks in brickwork
which often extend several courses below ground. Simple alterations in building and property
maintenance practices, such as providing exposed slab edges above ground and extending aprons of
slab around slab-on-ground dwellings will allow termite incursions to be reduced and detected,
providing that regular inspections take place.
Organophosphates and pyrethroids have since been offered as alternatives to the organochlorines
(Boyd et al., 2003). These chemicals are effective against termites for a much shorter time (< 5
years), due to the shorter lifetimes of these chemicals which break down relatively quickly and
therefore do not provide long-term protection. The need for more regular applications of the newer,
less-persistent chemicals results in an increased chance that householders and the pest control
operators will be more frequently exposed to the chemicals.
Persistence of Termiticides
Persistence describes the tendency of a chemical to survive in the environment without
transformation or loss (Boyd et al., 2003). Persistence in soils is usually described by the half-life
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(the time taken for the chemical to degrade to half of the original concentration). Degradation of a
termiticide may be by various routes, including microbial degradation (breakdown by micro
organisms), chemical degradation (breakdown due to reactions with air, water and oxygen, or other
chemicals the non-enzymatic pathway is very slow), and photo degradation (breakdown of
pesticides by sunlight). The half-life may be established under different conditions, varying pH or
soil type or in matrices other than soil (i.e. in water). The resultant values can therefore cover a
large range and may only be of use as a comparative or relative description, and can vary greatly
due to differences in soils, biota, climate and other factors. For this reason, soil half-life values
should be interpreted with caution. It should also be noted that most half-life data represent
breakdown of the parent compound and do not take into account biological effects of metabolites.
Generally:
•
•
•
Termiticides described as “persistent” have half-lives of >100 days
Termiticides described as “moderately persistent” have half-lives of 30–100 days
Termiticides described as “non-persistent” termiticides have half-lives of <30 days
The mobility of a termiticide in soil, air and water is influenced by its persistence and can be
defined by parameters, including sorption, water solubility and vapour pressure.
Sorption is the attraction between a chemical and soil, vegetation, or other surfaces, but often
simply refers to the binding of a chemical to soil particles. The sorption constant Koc describes the
potential to bind to soil particles, based on organic carbon content. Put simply, the higher the Koc
value, the greater the sorption (Table 1) (Bockting et al., (1993), Boyd et al., (2003), Laskowski
(2000) & Sabljic et al., (1995)). Differences in termiticide formulations and soil types can influence
sorption.
Termiticides may volatilise, with rates determined by the moisture content of the soil, and the
pesticide’s vapour pressure, sorption and water solubility. Volatilisation from moist soil is
described by the Henry’s Law Constant, calculated by the ratio of the vapour pressure of the
chemical to its solubility in water, which characterises the tendency for a pesticide to move between
the air and the soil water. The higher the Henry's law constant, the more likely it is that a pesticide
will volatilise. Vapour pressure is the tendency of a chemical to volatilise – a termiticide with a
vapour pressure of less than 1.0 x 10-8 mm Hg has a low tendency to volatilise, while those with
vapour pressures of more than 1.0 x 10-3 mm Hg have a high tendency to volatilise. Solubility in
water describes how much of a chemical will dissolve in water, usually measured at 20oC or 25oC.
Termiticides with high solubility are more likely to be mobile in the soil, they are likely to leach to
groundwater and be involved in runoff.
Current Chemical Termite Management in Australia
The withdrawal of the organochlorines as termiticides in Australia has by necessity encouraged the
introduction and investigation of new products and methods for termite management (Boyd et al.,
2003). Previously, because the organochlorines were so effective, there was apparently little
commercial incentive to develop new chemicals or barrier controls. Chemical control can be
divided broadly into preventative and curative measures. New buildings are treated with a chemical
barrier beneath and surrounding their slabs. Where access to slabs is not practical for under-slab
termiticide application, reticulation systems can be installed pre-construction, enabling repeated
application of termiticides over time. Where a termite infestation has occurred, chemicals may be
applied as spot treatments, sprays, baits or gases. There are termiticides registered for use in
Australia as varying formulations of synthetic pyrethroids (e.g. permethrin and bifenthrin),
organophosphates (chlorpyrifos), the chloronicotinyls (imidacloprid), arsenic trioxide (as a dust for
spot treatments), and recently a phenyl pyrazole (fipronil), along with wood preservatives such as
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Table 1 Reported Koc values of various termiticides in soil
Termiticides
Log KOC (Range)
Reference
Bifenthrin
5.06 – 5.47
Laskowski (2000)
Deltamethrin
4.7 - 6.39
Laskowski (2000)
Cyfluthrin
4.7 – 5.09
Laskowski (2000)
Fenpropathrin
4.13 – 4.98
Laskowski (2000)
Permethrin
3.91 – 5.74
Lambda-cyhalothrin
3.5 – 5.92
Bockting et al., (1993),
Laskowski (2000)
Laskowski (2000)
Cypermethrin
3.02 – 5-72
Laskowski (2000)
Chlorpyrifos
3.00 – 4.32
Bockting et al., (1993)
Fipronil
2.91
Boyd et al., (2003)
Imidacloprid
2.12 – 2.49
Boyd et al., (2003)
Mirex
6.00
Sabljic et al., (1995)
p-DDT
5.31
Sabljic et al., (1995)
Chlordane
5.15
Sabljic et al., (1995)
Aldrin
4.69
Sabljic et al., (1995)
Dieldrin
4.55
Sabljic et al., (1995)
Synthetic Pyrethroids
Other
Organochlorines
boron, copper, fluorine and creosote that are also used alone or in combination to prevent termite
attack.
Migration and Behaviour of Currently used Termiticides in Soils
Environmental variables are important, particularly in terms of transport, degradation and
volatilisation of termiticides. Following application, termiticides can be lost from the original
application site via lateral and vertical movement into surrounding soil and groundwater. It is
possible that these chemicals will be transferred to local biota and animals.
The movement of termiticides through soil largely depends on the physical properties of individual
chemical actives, the presence of water and biota and organic material, as well as the solvent/s that
have been used in the pesticide formulation. Soil characteristics, pH and the presence of organic
matter play major roles in determining the persistence and efficacy of chemicals. The half-life of a
chemical in the soil will depend on a combination of these factors and will be influenced by the
biota present. Sandy soils with low biota/low organic content and wet conditions generally result in
increased transport, whereas those with high clay and organic content minimise chemical migration.
The mineral content of the soil will influence degradation, by affecting adsorption rates or
catalysing decomposition. Termiticides, in particular the organophosphates, can be lost from the
soil through movement of volatiles into the air due to their significant vapour pressures at ambient
temperatures associated with lower Henry’s Law constants. Soil properties – organic content, silt
and clay content, pH and cation exchange capacity – are therefore important in affecting the
bioavailability and dispersal of termiticides.
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The Efficacy and Persistence of Currently used Termiticides
Australian evaluations of the organophosphates in soils suggest an effective life for chlorpyrifos of
7 to 12 years if covered, to as little as 4 years when exposed to the elements (Lenz et al., 1988), and
less than 3 years in tropical Australia. A field study of leaching and degradation of pesticides
(including chlorpyrifos, chlorthal dimethyl, fenamiphos, fenamiphos plus metabolites, linuron,
metalaxyl, metribuzin, prometryne, propyzamide and simazine) in coastal sandy soils (pH 5.3) in
Western Australia demonstrated that degradation rates vary widely between pesticides (Kookana et
al., 1995). Murray et al. (2001) examined the stability of chlorpyrifos in six Australian soil types.
Soil pH had no effect on the rate of degradation.
Testing of four soil types with six termiticide formulations indicate that soils have a significant
influence on the efficacy of the chemicals (Forschler and Townsend, 1996). Of the termiticides
tested (including chlorpyrifos, fenvalerate, cypermethrin and permethrin), all had concentrations
lethal to termites that were at least seven times lower in sandy soils than in sandy loam or sandy
clay loam (Forschler and Townsend, 1996).
A study of 6 termiticides (bifenthrin, chlorpyrifos, cypermethrin, fenvalerate, permethrin and
isofenphos) applied to different soil types in Texas, USA, demonstrated significant differences in
effectiveness (as measured by termite activity), bioavailability and residue (Gold et al., 1996).
Barrier efficacy tests of a range of termiticides (Dursban, Equity, Dragnet, Prevail, Biflex, Pryfon,
Demon, PP321 and Sumithion) in the USA indicate that while all formulations provide equal
protection against R. flavipes, C. formosanus was able to tunnel deeper into sand treated with
organophosphates than in sand treated with pyrethroids ( Su et al., 1993). Acidic soils with low clay
and organic content in Texas, USA, were found to be the most stable in terms of remaining
bioavailability of pesticides, while alkaline soils with high clay content and organic compositions
higher than 1% were least effective in retaining termiticide residuals over time (Gold et al., 1996).
Pyrethroids (bifenthrin, cypermethrin, lambda-cyhalothrin and permethrin) appear to provide longer
protection than organophosphates (chlorpyrifos, fenitrothion and isofenphos). According to 5-year
field trials in Florida, USA, against R. flavipes (Su et al., 1999), permethrin had the longest half-life
(21.9 months) of the pesticides examined. Microencapsulated formulations generally result in
longer persistence. In comparisons of different soil types treated with imidacloprid, pesticide effects
on R. flavipes were greatest in sand and reduced in silty clay loam soils (Ramakrishnan et al., 2000).
Little published Australian data are publicly available on the persistence and efficacy of other
termiticides.
THE DEVELOPMENT OF ALTERNATIVE APPROACHES
History of Termite Barrier Technology Research
Traditionally termite prevention calls for the use of an insecticide treated soil barrier to restrict
access to structural timber. The restriction of effective insecticides has led to development of
alternative techniques. Much of the research into the specifics of termite foraging has sought to
suppress populations with baits eg: (Chen & Henderson, 1996, Cornelius, 2003, Delaplane &
LaFage, 1989, French, 1991, Polizzi & Forschlerp, 1999, Waller et al., 1990) The traditional
concept of a barrier chemical treatment is being replaced by a attempt to maintain population
control through the use of toxic baits. (French, 1994, Potter, 1997, Su, 2002). However other
environmental and health conscious technologies are available and more are being developed.
Barrier technology involving inert gravel (Granitegard), stainless steel mesh (Termimesh) and
chemically impregnated polyethylene sheeting (Impasse) (Su et al., 2004) (Wege et al., 2003) are
all available for protection of houses from termites.
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The future of termite management in cities lies within an integrated approach that is able to take
into account preventative and retrospective treatments for termites and that is not only effective, but
is also economical, safe and environmentally friendly. Such treatments are likely to consist of
physical and chemical barriers, used in combination with resistant or preserved wood or steel
framing and according to the requirements of individual sites.
Integrated Barrier Approaches
An effective integrated approach needs to involve industry, government and consumer groups and
combine treatment and prevention programs with education, monitoring and collating data together
with research into new and better measures for termite management. There is a widely perceived
need for improvements in building design in order to prevent or reduce termite infestation along
with increased interest and demand for physical barrier systems. New building techniques and
designs, along with novel barrier systems to reduce exposure to termites are warranted, and further
research on termite foraging behaviour is required to facilitate the development of more effective
bait and monitoring technology. The efficiencies of different termiticide formulations need
investigating so that formulations to suit specialised purposes can be improved. Thus there are
many areas in which different management techniques including approaches based on integrated
pest management principles can be investigated.
Several requirements have been identified (Boyd et al., 2003):
•
More information is required on Australian termite biology, taxonomy and ecology. Ideally,
an understanding of the way in which termites forage, how they locate food sources, what
specifically attracts and repels them, and the mode and speed of infestations need to be
gained.
•
The risks of termite infestation need to be evaluated, both locally and nationally so that
susceptible or high-risk areas, structures and building types can be identified and preventive
measures taken in terms of design and construction. Building regulations and designs need
to be able to reduce or eliminate high-risk housing – and eliminate or reduce conditions that
are attractive to termites and/or facilitate termite infestation.
•
Further education is required for homeowners, builders, designers, legislators and landscape
designers so that they can reduce the risk of infestation through the avoidance of practices in
landscaping and design that inadvertently favour termites i.e. ensuring good under-floor
ventilation, which discourages termite activity, not stacking timber or building up soil
against or near buildings, reducing timber use where inspection for termites is difficult, and
not building wooden in-ground structures (e.g. untreated timber retaining walls) close to
houses.
•
There needs to be a specific focus on the creation of alternative barriers for the range of
wooden structures that need protection. The focus needs to take account of the current
limitations of physical barriers and monitoring stations which may be avoided by termites
and overcome the loss of activity associated with short-term response chemicals which have
replaced the more hazardous organochlorine compounds. An innovative approach to barrier
design is needed that seeks to incorporate the specific features of slow release chemicals,
e.g. based on natural products which are more acceptable to the environment and public
health.
•
Since most termite-related damage to timber occurs from subterranean termites, preventative
measures rely heavily on site housekeeping and the establishment of physical or chemical
barriers to stop the termites getting into the premises or timber from the underlying soil.
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Once the termites have been found in wooden structures, a range of physical and chemical
techniques are available to treat and eliminate (or control) the infestation. There is a need for
a reliable long-term, maintenance-free method of preventing termite infestations that poses
little or no risk to human or environmental health.
As a consequence research at the University of Queensland has commenced to look into the
behaviour of termiticides, current and potential, in Australian soils and under Australian conditions.
Open and collaborative communication between stakeholders needs to be maintained and widened
so that the concerns of each group are addressed.
PHYSICAL RESISTANCE OF MATERIALS TO TERMITE ATTACK
Issues of Termite Attack
The large body of work describing biologically active repellent or attractive plant volatiles is in
stark contrast to research investigating physical defences of plants (Sanson et al., 2001). What
physical characteristics make a material difficult for termites to attack remains largely unanswered.
Studies addressing the issue typically investigate the quality of hardness or general material type. It
has been suggested that termites will only damage materials less hard than mandibles of termites
(Potter, 1997), yet we are unaware of any quantification of termite mandibular hardness and
contributing factors. Because mandibular hardness is associated with high concentration of zinc and
Figure 2 Experimental apparatus to study termite attack on a synthetic barrier material (photo by A. Stewart)
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other metals nutrition may have an impact on the deposition of metals (Morgan et al., 2003).
Cornitermes cumulans cinereus author mandibles were found to contain large quantities of
manganese but not zinc (Fawke et al., 1997).
More understanding of the mechanics of micro-mechanics of mandibular action is needed to predict
the resistance of synthetic materials is to be made. Deligne (1999) described a plane like carpenters
tool on the mandible of workers and suggested a mechanism by which it is used. A scraping action
would suggest that resistance to wear may be a critical material property. Although in some
materials, wear resistance is related to hardness, in others, depending on the wear mechanism,
issues of toughness and fatigue resistance are the critical parameters. Moreover, quantification of
the magnitude and mode of force application by mandibular action is required to establish bench
marks for material properties. The mechanical force applied by mandibles can be measured, as
described for several Carabid beetles and a heliothine moth (Navon et al., 1992, Wheater & Evans,
1989). Using a similar methodology we have measured the mandibular closing force for several
species of termites. The response of synthetic materials to surface forces of a magnitude exerted by
termites is fundamental to understanding their mechanism of resistance to termite damage (Figure
2).
Synthetic Materials
Research into synthetics designed to protect timber should take into consideration the possibility
that termites will be able to detect wood through the barrier, and consequently affect foraging
behaviour. Early laboratory work that investigated the resistance of plastics to termite attack
involved exposure of termites to test materials without any direct stimulus to attack, such as
Figure 3 Termite damage to synthetic material without termiticide present (photo by A Stewart)
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providing a barrier to a food source (Gay et al., 1955, Gay & Wetherly, 1969). Lenz (1994)
examined the effect of food sourced on the other side of barrier in laboratory assays field trials,
inevitably involving the presence of wood, (Nakamura et al., 1985). These studies on resistance of
various materials are performance based and provide little idea of exactly how quickly termites can
damage materials or what causes the apparent threshold of material toughness to stop damage.
Damage to wood is commonly given as a volume or weight removed per termite weight per unit of
time. This, however, hasn’t been attempted for damage to synthetics (Figure 2).
It is generally agreed that a high degree of hardness is required to impart resistance to termite attack
(Arkell et al., 1994, Nakamura et al., 1985). Unplasticised polyvinylchloride is hard enough to repel
termites, consequently various UPVC products with a hardness of Shore D 70 or higher are used in
Australia for protection via plumbing holes in the concrete slab (Ewart, 2001). Nakamura et al.,
(1985) found nylon with hardness greater than Shore D was 72 to impart resistance in a very thin
layer < 0.3 mm thick. Sheets thicker than 0.33 mm are more resistant from edge chewing than
thinner sheets.
The research currently being undertaken at the University of Queensland is approaching the
problem of barrier resistance by seeking to understand how termites attack various synthetic
materials via mandible action (Figure 3). This is different to studies undertaken to date and will lead
to an ability to provide criteria for barrier material selection.
TERMITE REPELLENCE
Repellence is generally described as inability of termites to tunnel through treated substrate (Bläske
& Hertel, 2001, Cornelius et al., 1995, Zhu et al., 2001) or as a tendency of termites to plug tunnels
contacting undesirable substrates (Staples & Milner, 2000, Su et al., 1982), by aggregation, or lack
of, on impregnated substrates (Sbeghen et al., 2002) and antifeedent properties of impregnated
wood (Escoubas et al., 1995). All of these descriptions rely on a performance variable and the exact
mechanism of repellence in not clear. Three types of insecticide have been described: those that
repel immediately; those that kill quickly and the dying termites repel; and those that act slowly
such that the termites don’t die in situ (Su et al., 1982). The first two types would rate as repellent in
soil penetration assays.
Various alternative compounds have the potential to repel termites if presented in a barrier system,
the lower volume of chemical required in thin barrier technology may allow the use of previously
prohibitively expensive or unstable compounds. Alternatives include Catnip oil (Peterson & EmsWilson, 2003), plant derived quinones (Ganapaty et al., 2004), semiochemicals extracted from ants
(Cornelius & Grace, 1994), monoterpenoids (Cornelius et al., 1997), pathogenic fungi conidia
(Staples & Milner, 2000), diterpenes (Lajide et al., 1995a), and extracts from seeds and fruits
(Lajide et al., 1995b).
A variety of currently used insecticides have repellent properties including silaneophane,
fenvalerate, bifenthrin, cypermethrin and permethrin all induce avoidance between 1 and 10 ppm
(Su & Scheffrahn, 1990). Bifenthrin performed extremely well with C.formosanus at low
concentrations; 1 ppm reducing tunnelling in adjacent soil 3 cm away from treated soil (48 hours)
(Smith & Rust, 1990). However C. formosanus can tunnel through 10ppm if the thickness of the
treated soil is 0.15cm (Su et al., 1995). The desired concentration of termiticide in thin synthetic
barrier is ambiguous. Bifenthrin is repellent to termites, not unlike other parathyroids (Su et al.,
1999). Soil was repellent at 1 % bifenthrin but the effect of repellence may have been through
immobilisation of termites attempting to construct tunnels (Smith & Rust, 1990).
Laboratory response in terms of ability to tunnel into treated soils is generally a good reflection of
results obtained from field populations, although threshold concentrations may be higher in the field
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Environment 25– 12
in some cases, termites were more aggressive towards the treated soil in the laboratory. Interestingly
the threshold of the repellent permethrin in the laboratory (1ppm) was much lower than what field
populations (100ppm) could penetrate (Su et al., 1997). Soil from actual treatment sites has been
used in assays (Su et al., 1993). Increased population density can increase the ability of termites to
penetrate a substrate treated with an insecticide (Jones, 1990). Differing depths of soils impregnated
with Dursban and other insecticides results in variation in termites ability to penetrate the barrier to
the other side (Gahlgoff & Koehler, 2001, Su et al., 1995). This may not be the case in situations
where the insecticide is more repellent.
THE FUTURE FOR AUSTRALIAN CITIES
The problems associated with termites in Australian cities are clearly identified and requiring
innovative approaches. The identified large costs to buildings and other wooden structures from
termite damage reveals that termites remain part of the urban environment of Australian cities
following construction. The utilisation of less-persistent termiticides following the phase-out of
organochlorines has created a less desirable situation of needing to reapply chemicals every few
years to maintain barrier protection giving rise to environmental and public health consequences.
The future lies with well developed termite management strategies that incorporate the kind of
research that will lead to alternative barriers giving protection of wooden structures against termite
attack.
Urban cities & termite attack
Environment 25– 13
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